The invention relates to a device for hydraulically adjusting the angle of rotation of a shaft to a driving wheel, especially of the camshaft of an internal combustion engine.
Such a device is known, for example, from U.S. Pat. No. 4,858,572. In the case of a device of this type, an inner part is connected, so that there cannot be any mutual rotation, with the end of the camshaft, which has at its outside several radial slots, which are distributed over the periphery and in which wing elements are guided radially displaceably. This inner part is surrounded by a cell wheel, which has several cells, which can be acted upon hydraulically and are divided by the wings into two pressure spaces acting against one another on these cells. By the action of pressure on these pressure spaces, the cell wheel, as a function of the pressure difference, can be twisted relative to the inner part and with that, to the camshaft. Moreover, in the cell wheel in each of two radial boreholes in defined angular positions, a piston, which can be acted upon hydraulically and, in the assigned end position of the device, can be pushed into a radial recess of the inner part. These pistons are acted upon by compression spring elements in the direction of the inner part and can be shifted in the opposite direction by hydraulic action on the boreholes. By means of these pistons, which are acted upon by springs, the device is to be locked in one of its two end positions as long as the pressure for acting upon the pressure spaces has not reached a defined level. Only when a particular pressure level is reached are the pistons pushed back against the action of the compression springs and the inner part can be twisted relative to the cell wheel. Rattling noises, for instance, which are due to changing torque loads during the starting up and operation of the internal combustion engine, are to be avoided with such a devise during the starting up of the internal combustion engine. Furthermore, from the DE 39 22 962 A1, a device is known for hydraulically adjusting the angle of rotation of a camshaft to its driving wheel, for which the inner part is provided with fixed, radially extending bridges. Between the bridges of the inner part and the opposite bridges or walls of the cell wheel, compression springs are mounted which, when the pressure acting is reduced, move the inner part relative to the cell wheel into one of the two end positions.
These known devices for hydraulically adjusting the angle of rotation of a shaft to its driving wheel have the disadvantage that, during the operation of such a device, due to the impact between the bridges of the inner part and the adjoining walls or bridges of the cell wheel when one of the two end positions is reached, high stresses and increased development of noise may occur. This increased formation of noise has a disturbing effect during the operation of such a device. Moreover, the impact load of the bridges upon reaching the end position and resulting from the action of pressure and from the torque, acting from the driving mechanism on the cell wheel, can lead to appreciable stresses which under some circumstances can have a negative effect on the service life of such a device.
In contrast to the above, it is an object of the invention to improve a hydraulic adjustment of the angle of rotation of a shaft to its driving wheel so that increased impact loads are avoided when one of the two end positions is reached and that the thereby caused noise formation and component stress are reduced.
Pursuant to the invention, this objective is accomplished. If the change in the rotational position is damped hydraulically by integrated damping means before one of the two end positions is reached, the mechanical impact load is reduced distinctly. By means of this hydraulic damping before the respective end position is reached, it can be ensured that, in particular, the relative speed of the two components to one another is clearly reduced. The energy, which must otherwise be converted during the undamped approach to the end position at the stop can thus be reduced to a large extent by the hydraulic damping. In this connection, it is particularly advantageous if the hydraulic dampening is designed in the form of an end position damping, which becomes active only when the end position is approached otherwise does not affect the adjusting process.
The integrated hydraulic damping can be constructed particularly advantageously in the form of a hydraulically acting damping throttle.
An integrated damping, which becomes effective when the respective end position is approached, can be attained in a particularly advantageous manner, if a throttle chamber, in which a pressure medium is enclosed before the throttle position is reached, is constructed between the bridges of the inner part and the bridges of the cell wheel. By means of such a throttle chamber, which can be constructed between components moved relative to one another, an angularly accurate assignment of the start of the dampening or of a damping, setting in when a defined position is reached, can be set by suitable size dimensions. With that, it is possible to ensure in a particularly advantageous manner that the adjusting process takes place over the largest possible angular range.
An end position damping, which is particularly advantageous with respect to the mechanical stressing of the components, results when the throttle chamber pressure can be relieved over a defined throttle gap. As the end position is approached, the pressure medium, enclosed in the pressure chamber, can emerge throttled relatively severely over this throttle gap, so that excessive damping is avoided. Moreover, by constructing the sealing gap appropriately, it can furthermore be ensured that the mechanically limited end position can be reached in any case. Disadvantageous spring effect can thus be prevented effectively.
Such a throttle chamber can be constructed particularly advantageously, if in each case a recess is constructed in one of the respectively adjacent bridges and a corresponding extension in the other bridge. As the two adjacent bridges approach one another, the projection dips into the recess, so that the opposite regions of the wall close off the throttle chamber or form the throttle gap by means of their overlap.
Further advantages and advantageous further developments of the invention arise out of the dependent claims and the specification.
An example of the invention is described in greater detail below and in the drawing, in which